Static limitation in radio receivers



March 5, 1940. P. M. HAFFCKE STATIC LIMITATION IN RA DIO RECEIVERS Filed March 12, 1938 2 Sheets-Sheet 1 TO RECTIFIER T0 AMPLIFIE e 1 mm fin T N 9 NH M 3 m M T .w M .w Pm b E m mi W L: n R E m L 8 P M J A M u March 5, 1940; V p HAFFCKE 2 ,192,189.

STATIC LIMITATION IN RADIO RECEIVERS Filed March 12, 1938 2 Sheets-Sheet 2 1 1. EL. 7 i5- JI-J NON-LINEA AMPFR. v 4

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/63 INVENTOR 4,4. Philip M Haffche ATTORNEY Patented Mar. 5, 1940 UNITED STATES PATENT OFFICE 15 Claims.

(Granted under the act oi March 3, 1883, as

amended April 30, N28; 370 0. G. 75'?) This invention relates to means for suppressing the effect of static components in energy rel removed from the signal frequency to permit frequency discrimination between the disturbingsurges and the signal;

To provide means normally inactive to permit a signal to pass through a radio receiver tube but is rendered active by excessive surges of energy to eifect plate current cut-off during periods of excessive amplitude;

To provide means for changing excessive amplitudes into harmonics that will be eliminated by subsequent tuned stages;

To improve the operation of code receivers by diminishing the effects of excessive amplitude energy thereon.

In the drawings: I I

Fig. 1 depicts a system for changing the bias on the cathode and on a normally inactive grid in a vacuum, tube to reduce theplate current when excessive surges are received;

Fig. 2a shows a normal signal wave and a wave of excessive amplitude, 2b illustrates the form of the output wave of normal amplitude and the form of the output for, excessive amplitudes, and 2c shows the voltage wave across the rectifier due to the excessive amplitude;

Figs. 3, 4, and 5 show various "arrangements of means acting as a variable impedance across the input of a vacuum tube network and means for applying control potential to the suppressor grid;

Fig. 6 also shows means for changing the potential on the suppressor grid to control the output of the tube;

Fig. 7 shows a different type of larly to Fig. 6;

Figs. 8 and 9 disclose other networks for the same purpose utilizing the same type of tube as in Fig. 7;

Fig. 10 shows a modification in which the control voltage is applied to the signal grid.

I have found that with many static suppressing systems where a signal is superimposed upon a constant plate current the effect of static will, in many cases, cause actual plate current cut-off, or at least such a rapid change in plate current tube used simithat the effect of such changes in the following,

the static itself, when the system is adapted to code reception.

The ideal system, of course, would be one in which the output of the suppressing stage will not carry anything other than the desired signal, that is, during periods when there is no code character present, no plate current will be flow- Although such a system has been sought and various balancing circuits tried out, no successful means has been produced effectively to segregate static from a desired code signal, although partial success seems to be obtained by various limiting systems that cut off the peaks of abnormally high amplitudes. In any event such a system cannot hold the inter-character static to below the level of the signal amplitude.

The present systemis radically different from any other of which I know, both in theory and in actual operation, is simple and adds little to the complications of operating the receiver, yet any instantaneous surges of static of high amplitude as compared to the average readable code signal are reduced to a minimum even during periods of no signal such as inter-character spaces.

Under ideal receiving conditions for code messages, there must be in the antenna system no strong parasitic disturbances present at the frequency of the desired signal, or within less than, say, 200 cycles of the desired signal frequency. If no interfering station is in operation within the above limits good aural reception is afforded on receivers of modern design. However, such a condition is seldom found in actual practice as parasitic and atmospheric disturbances are nearly always in evidence when the sensitivity of a receiver is set to a high level. Such parasitic disturbances now assume extreme proportions in amplitude and are as a rule many times stronger than the desired signal, though perhaps of short duration.

Now, if we convert a large percentage of these higher amplitude surges to some frequency considerably removed from that of the desired signal, it would make possible further discrimination between the heavy static surges and the signal wave on the basis of difference of frequency. This is the underlying principle involved in the present invention and is distinct and remote from those systems for static suppression in radio telephone reception wherein plate current is present and flowing during no signal intervals, and is cut to zero during periods of excessive input potentials.

To accomplish the end of no plate current change at the desired periods of "no signal", I operate the tube Just at or slightly beyond the point of plate current cut-ofl, commonly known 8 as Class B, Class BC or Class C operation. Thus,

when no signal is present there is no plate current flowing because the signal grid is biased to just below plate current cut-off, and when the signal does come in this grid is caused to swing 10 into the working range and thus allows the plate current to flow during periods of normal signal strength and amplitude on the positive half of the cycle only, somewhat'similar to Class C operation. However, when parasitic and atmospheric l3 surges of extreme amplitudes are introduced into the receiver, a rectifier andits associated circuit cause another grid situated in the electron path between cathode and anode but normally inactive, to cause plate current cut-off during such periods 30 of excessive amplitudes even though the signal grid would allow electrons to pass while the desired signal is on". This naturally causes a hole in the wave but this action. is occurring on the individual radio frequency wave and leaves two 28 smal waves, of shorter base line than the funda- 80 circuits and thus will become far less effective in shocking the following stages into excitation than is the case with an ordinary limiting system, because of the wave shape presented to the following transformers and the characteristic in- ,herent in any circuit containing an inductive factor, to a wave of fiat top form when, although some harmonic components will be present, they will not be generated as efficiently as when the wave presented to the primary is of the form 40 produced by, the present system, hereinafter discussed in detail.

Referring now to Fig. 1, the radio frequency tube I receives'input potential on grid H from coupling transformer |2 across the primary of 5 which a coupling inductance I3 is connected to supply radio frequency energy to rectifier tube H which has a coupling inductance l5 and a resistor IS in series with its anode I1 and cathode l8. The cathode |8 has impressed upon it a 50 suitable small positive potential through resistor I9 to prevent rectifying action so long as the amplitude of the energy impressed upon inductance I5 is of less than a predetermined value. Inductance |3 acts as a variable impedance 55 across the primary coil of transformer |2 when rectifier tube I4 is passing current and so exercises a limiting action upon the input to grid The high potential side of resistor I6 is connected by wire to cathode 2| of tube It), while the low potential side of resistor I6 is connected by wire 22 to grid 23, which grid is normally inactive and exerts no effect upon the electron stream. A positive potential is applied to cathode 2| through a portion of variable resistor 24 whereof the low 05 voltage side is grounded at 25, whereby tube III is biased somewhat below cut-off at no signal. Capacitance 26 is connected from the cathode lead to ground in shunt with that portion of resistor 24 that is effective in biasing grid H, and

7c is of large capacity to insure a fairly constant bias on the grid.

Energy of normal signal amplitudes, as at 28 in Fig. 2a, is transferred through tube ill to the g following stage through a tuned output network I 21, the output Wave being as shown at 29 in Fig.

2b, due to the bias on tube I0 which results in substantially Class 0 operation. When an excessive surge, as at 30 in Fig. 2, is received the rectifier l4 passes current, resulting in a decrease of the impedance of inductance |3 due to the fact that the bias on rectifier I4 is overcome and the rectifier is caused to pass current, thus reducing the input to tube H). The IR drop across resistor l8 due to the rectifier current impresses increased positive potential on cathode 2| and negative potential on grid 23, thus diminishing still more the current through tube l0, and if amplitude of the surge is sufilciently great,

as at 30 in Fig. 2a., the tube I0 .is swung to cut-oil represented by the fiat top will be taken out in i the following stages. Since no waves of amplitude much in excess of the normal signal amplitude pass tube H), the other stage, will not be shocked into excitation during no signal intervals and if the amplitude is sufilciently great the wave will be thrown off as higher harmonics and not reach the latter stages.

Fig. 3 is in general similar to Fig. 1 but in this case the normally inactive grid is the suppressor grid 30. Here the inductance I3 is coupled to input inductance 3| of an amplifier tube 32 so biased as to amplify disproportionately the higher amplitudes in the input energy as disclosed in my copending application Serial No. 87,404, filed June 26, 1936. Output primary coil 33 is coupled to input secondary I5 of rectifier N that is connected to cathode 2| and normally inactive suppressor grid 30 of tube It) to function as above described. An additional limiting action is secured by the connection of a rectifier, 34 in parallel with the primary coil of input transformer l2, whereby excessive amplitudes are bypassed and do not so strongly affect the operation of tube l0.

In Fig. 4 the arrangement is the same as in Fig. 3 except for the connection of the rectifier 35, which is connected in parallel with the secondary coil of transformer l2 with the cathode lead being disposed to include a portion of biasing resistor 24 in the rectifier circuit, whereby the rectified current flowing through tube 35 impresses additional IR drop upon control grid While at the same time the cathode of the bypass rectifier 35 is given the desired positive bias to prevent rectification at normal signal amplitudes. I

In Fig. 5 the by-pass rectifier '36 is coupled by a coil 31 to inductance 38 that is in parallel with the primary of input transformer |2. It is obvious that when rectifier 36 draws current the impedance of the input circuit is much reduced and high amplitude energy is'by-passed and thus the input to tube I0 is reduced.

It is to be noted that in the arrangement shown in Fig. 1 the normally inactive grid is between the cathode 2| and the control grid whereas in Figs. 3, 4 and 5 thecontrol grid H is between the cathode 2| and the normally inactive grid 30,

and it is therefore preferable that some amplification of the radio frequency energy take place before rectification in tube l4, owing to the greater distance of the normally inactive grid from the cathode.

In Fig. 6 the control potential derived from the rectified current flowing through the rectifier tube 39 is applied between the cathode 2| and suppressor grid 30. of the tube In. Otherwise, this network is very similar to that'of Fig. 1.

Fig. 7 discloses the network arrangements for applying the present invention to a tube of the type known as 6L7. The control grid'40 of tube 4| is connected to the secondary of input transformer 42 across the primary of which. is connected a non-linear amplifier 43 to amplify disproportionately high amplitude waves'-, the output of amplifier 43 being coupled by inductance 44 to inductance 45 in the anode-cathode circuit of rectifier 46. The IR drop across resistor 4! in the rectifier circuit is applied to normally inactive grid 48 and cathode 49 of tube 4! to exercise control over the current through tube 4| in the manner above described. Tube 4! is biased to cut-off or slightly below at no signal and operates substantially as a Class C or BC amplifier.

The embodiment of my invention disclosed in Fig. 8 differs from that in Fig. 7 in that the grid 48 is here the control grid and the grid 40 is the normally inactive grid to which control voltage is applied.

Fig. 9 is like Fig. 8 with the addition of a resistor 59 in series with accelerating grids 50 that are positively biased and hence normally accelerate the electrons in the electron stream but when the electron stream increases above a predetermined value the current flowing from cathode 49 to grids 56 produces a potential drop across resistor 59 and reduces the potential on grids 56 and thus applies an additional limiting action to the electron stream to cut down the output current.

It is to be noted that the preliminary limiting action impressed upon the input changes the wave form of the input energy so that the action of the normally inactive grid, when rendered active by excessive amplitudes of received energy, is much more effective in throwing the high amplitude waves to higher harmonics that may be taken out by the subsequent tuned stages. I

Fig. 10 illustrates an application of the principle of this invention wherein the static controlling action is exercised through the signal grid 6| of tube 62. Tube 62 is given a Class C bias by battery 63 and a resistance 64 is in series with cathode 65 and grid 6!, the signs and adjacent the terminals of resistance 64 indicating the sense of the potential drop therein due to current from rectifier tube 66. Coil 44 receives the output of non-linear amplifier 43 and is coupled to coil 61 in series with anode 66 and cathode 69 of rectifier tube 66, the coil 61 being so poled with respect to input coil 16 of tube 62 that anode 68 is made positive, when the rectifier 66 functions, at the same time grid 6| of tube 62 is swung positive. Reception of an excessive amplitude surge that would swing grid 6| strongly positive causes rectifier 66 to pass current and.

the IR drop resulting from passage of this cur-l rent through resistor 64 impresses upon grid 6l 'suflicient negative potential to neutralize the excessive positive potential.

It will be understood by those skilled in this art that for operation at some frequencies the by-pass condenser in parallel with the resistance in the rectifier circuit may be omitted if the time lag introduced thereby is undesirable.

In some instances it is preferable to leave the for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. In combination, a radio energy transfer device having a primary inductance and a secondary inductance; a vacuum tube having an anode, a cathode, a control grid, and a normally inactive grid; means connecting said control grid and said cathode to opposite sides of said second-\ ary inductance," means for biasing said tube atv least to cut-off including a variable resistance whereof a portion is included between said cat ode and said secondary inductance, a large ca-, paeity condenser connected in shunt with said portion of said resistance, a first inductance connected across said primary inductance, a second. inductance coupled with said first inductance, a rectifier tube having an anode and a cathode, means including a second resistance connecting the cathode of said rectifier to one side of said second inductance, means connecting the anode of said rectifier to the other side of said second inductance, means connecting the high potential side of said second resistance to the cathode of said vacuum tube, means connecting the low potential side of said resistance to said normally inactive grid, means including a third resistance to apply'positive potential at said low potential side of said second resistance, a ground connection to the low potential side of said variable resistance and a tuned output circuit connected to the anode of said vacuum tube.

2. A vacuum tube network, comprising a vacuum tube having a plurality of electrode elements including a cathode and a normally inactive grid, radio frequency input means connected to said cathode and to another of said electrode elements, a rectifier tube having an anode and a cathode, means including a resistance connecting said anode and cathode of the rectifier, means to maintain on said vacuum tube a substantially constant bias at least to cut-off, means connected across said input means to transfer radio frequency energy to said rectifier, means to bias said rectifier to prevent operation thereof when the said radio frequency energy is of less than a predetermined amplitude but to permit said rectifier to operate when said predetermined amplitude is exceeded, means connecting the high voltage side of said resistance in the rectifier circuit to the cathode ofv said vacuum tube and means connecting the low voltage side of said resistance to said normally inactive grid.

3. A vacuum tube network, comprising a vacuum tube having a plurality of electrode elements including a cathode and a normally in active grid, said tube being biased to cut-off at no signal, radio frequency input means connected to said cathode and to another of said electrode 1 value of said potential diiference to the cathode of said vacuum tube, and means to apply the low potential value of said potential difierence to said normally inactive grid.

4. A vacuum tube network, comprising a vacuum tube having a plurality of electrode elements including a cathode and a normally in active grid, said tube being biased to cut-oil? at no signal, radio frequency input means connected to said cathode and to another of said electrode elemnts, means to divert a portion of the energy from said input means, means coupled to said diverting means to effect disproportionate amplification of high amplitude components of said diverted energy, rectifying means controlled by the said disproportionately amplified components including an element across which a potential difference is set up by the rectifiedpurrent, and

means to apply to said cathode the potential at the high potential terminal of said element and to said normally inactive grid the potential at the low potential terminal of said element 5. A vacuum tube network, comprising a vacuum tube having a plurality of electrode elements including a cathode and a normally inactive grid, radio frequency input means connected to said cathode and to another of said electrode elements, means to divert a portionof the energy from said input means, means coupled to said diverting means to effect disproportionate amplification of high amplitude components of said diverted energy, rectifying means controlled by the said disproportionately amplified components including an element across which a potential difference is set up by therectified current, means to apply to said cathode the potential at the high potential terminal of said element and to said normally inactive grid the potential at the low potential terminal of said element, and means connected across said diverting means and responsive to said high amplitude components to act as a low impedance shunt during the incidence of such high amplitude components.

6. A vacuum tube network, comprising a vacuum tube having a plurality of electrode elements including a cathode, a control grid and a normally inactive grid, radio frequency input means connected to said cathode and said control grid, means to divert a portion of the energy from said input means, means coupled to said diverting means to effect disproportionate ampliflcation of high amplitude components of said diverted energy, rectifying means controlled by the said disproportionately amplified components including an element across which a potential diiference is set up by the rectified current, means to apply to said cathode the potential at the high potential terminal of said element and to said normally inactive grid the potential at the low potential terminal of said element, rectifying means in shunt across said cathode and said control grid responsive to excess amplitudes of input energy to by-pass a portion of said excess amplitude energy, and impedance means in the circuit of said rectifying means and between said cathode and said control grid whereby the current through said rectifier impresses additional negative bias on said control grid.

7. In a method of operating a vacuum tube network comprising a vacuum tube having electrode elements including a cathode and a normally inactive grid and input means coupled to said tube, the steps of biasing said tube to cutoff, shunting a portion of the received energy a immediately ahead of said input, applying said shunted energy to cause rectified current to flow when the amplitude of the received energy exceeds a predetermined magnitude, said shunted ,energy being subtracted from the input to the tube, utilizing said rectified current to produce a potential difference, and applying said potential difierence-to make said cathode more positive and said normally inactive grid negative.

8. In a method of operating a vacuum tube network comprising a vacuum tube having electrode elements including a cathode and it normally inactive grid and input means coupled to said tube, the steps of biasing said tube to cutoii, shunting a portion of thereceived enery immediately ahead of saidinput, disproportionately amplifying high amplitude components of said shunted energy, applying said amplified shunted energy to cause rectified current to flow when the amplitude of the received energy exceeds a predetermined magnitude, said shunted energy being subtracted from the input to the tube, utilizing said rectified current to produce a potential difference, and applying said potential difference to make said cathode more positive and said normally inactive grid negative.

9. In a method of operating a vacuum tube network comprising a vacuum tube having electrode elements including a cathode and a normally inactive grid and input means coupled to said tube. the steps of biasing said tube tocut-ofi, impressing upon the input energy into said tube a limiting action whereby to produce harmonics and flatten the top of the energy wave, drawing energy from the same source as said input energy and deriving rectified current from the energy thus drawn, and applyingv said rectified current to interrupt the current through said tube during the incidence of energy of amplitudes above a predetermined maximum, thereby breaking up each wave of such excess amplitude into two waves of a higher harmonic and of amplitude not in excess of said predetermined maximum amplitude.

10. In a method of operating a radio receiver.

to prevent flow of plate current during no signalintervals and shocking of the last stagesinto excitation, said receiver comprising a stage including input means and a-vacuum tube having a cathode and a normally inactive grid, the steps of biasing said tube to cut-oil, diverting energy from the signal channel of said receiver immediately ahead of said input means and disproportionately amplifying high amplitude components of said diverted energy, rectifying said disproportionately amplified energy and applying said rectified energy to produce a potential difierence, applying said potential difference to said cathode and said normally inactive grid to break up waves having an amplitude in excess of a predetermined magnitude into two waves of a-hi'gher harmonic and of amplitude not in excess of said predetermined magnitude, and blocking out said higher harmonic waves in a subsequent tuned stage.

11. In a method of operating a vacuum tube network comprising a vacuum tube having a plurality of electrodes including a cathode and more than one grid, the steps of biasing said tube to cut-ofi, maintaining one of said grids normally inactive, utilizing excess amplitude of waves of received energy to apply a limiting action to the transferof energy through said-tube during the incidenceof such waves of excess amplitude, and further utilizing such excess amplitude energy to make said cathode more positive and render said normally inactive grid negative, whereby each tov 1 portion of said energy when the amplitude'thereof is in excess of a predetermined value, rectifying said non-linearly amplified energy, and passing said rectified energy through said resistor whereby to reduce the potential on said grid 3 when said :grid tends to swing excessively positive due to said excess amplitude.

13. Amethod of operating a vacuum tube 11 a work that-includes a vacuum tube and an input circuit therefor, comprising the steps of biasing said tube at least to cut-oi! at no signal, collecting radio energy, feeding atleast a portion of said energy to said circuit, diverting ahead of said circuit a'portion of said energy when the amplitude thereof isin excess of a predetermined value. non-linearly amplifying said diverted portion. rectifying said non-linearly amplified portion.

and utilizing said rectified energy to produce a potential drop in said circuit opposed to the energyfed into said circuit.

14. A method of operating a vacuum tube network that includes a vacuum tube and an input circuit therefor, comprising the steps of biasing said tube at least to cut-ofl at no signal, collecting radio energy, feeding at least a portion of said energy to said circuit, rectifying another portion of said energy when the amplitude thereof is in excess of a predetermined value, and uti lizing said rectified energy to produce a potential drop in said circuit opposed'to the energy fed into said circuit.

15. In a radio receiver, a vacuum tube having input electrodes, circuit means connecting said electrodes including a resistor and means to impress on said tube abias at least to cut-ofl? at no signal, a rectifier tube including electrodes con nected across said resistor, and means responsive to excessive amplitudes of received energy to supply to said rectifier energy so poled-that current from said rectifier produces in said resistor a potential drop opposed to the input potential on said electrodes.

PHILIP M. HAFFCKE. 

